Field of the presently disclosed and/or Claimed inventive concept(s).
This invention includes embodiments relating to titanium dioxide (TiO2) based scrubbing granules, and methods of making and using such TiO2 scrubbing granules. Particularly, the invention includes embodiments relating to TiO2 based scrubbing granules with sodium aluminate binder and various methods of using such TiO2 based scrubbing granules during TiO2 production; and embodiments relating to unsintered TiO2 based scrubbing granules with inorganic metal binder and various methods of using such TiO2 based scrubbing granules during TiO2 production
Background of the presently disclosed and/or Claimed inventive concept(s)
Generally, TiO2 particles are produced by a chloride or a sulfate process. In the chloride process, titanium tetrachloride (TiCl4) undergoes vapor phase oxidation to form TiO2 particles as part of a hot gaseous suspension. The hot TiO2 particles, along with other gaseous by-products in the hot gaseous suspension, are passed from a reactor to a heat exchanger. The hot gaseous suspensions are cooled by contact with the inner surface walls of the heat exchanger which have temperatures less than that of the hot gaseous suspension. As the hot TiO2 particles are cooled, the TiO2 particles may deposit on the inner walls of the heat exchanger or reactor and form adherent layer deposits. The adherent layer deposits lower heat transfer efficiency through the inner walls of the heat exchanger and thus reduce cooling efficiencies. Such inefficiencies affect the quality of the formed TiO2 particles and the efficiency of the downstream finishing and surface treatment steps.
In attempts to remove adherent layers, “scrubs” such as sodium chloride (NaCl), silica sand, calcined TiO2 particles, sintered TiO2 particles have been added to the hot TiO2 pigment particles flowing through the reactor and heat exchanger. For example, NaCl scrubs such as U.S. Pat. No. 3,511,308 increase viscosity of TiO2 slurry, thereby lowering the throughput rate in the finishing step. Silica sand scrubs introduce contaminants into the process and may also increase reactor wear and downtime of the process equipment, e.g., the reactor, the heat exchanger, etc.
U.S. Pat. No. 5,266,108 discloses calcined TiO2 scrubs typically prepared by heating the TiO2 particles to a maximum temperature of approximately 1000° C. Unfortunately, such high temperatures decrease the surface area of most known TiO2 scrubs and makes size of scrubs difficult to control. Calcined or sintered TiO2 scrubs also have one or more of the following disadvantages. Calcined or sintered TiO2 scrubs contaminate the finished TiO2 pigments, thus requiring additional processes. Calcined or sintered TiO2 scrubs are difficult to reduce to pigmentary size; and calcined or sintered TiO2 scrubs can affect the dispersion and/or effectiveness of TiO2 finishing processes.
Thus, a need still exists for improved scrubbing mediums, and method of making and using such improved scrubbing mediums.